JavaScript Utility: Saturn's Moons

Sky & Telescope's Saturn's Moons JavaScript utility, which will open in a new browser window, shows the positions of Titan, Rhea, Dione, Tethys, and Enceladus for any date and time from January 1900 to December 2100.

Here is what the routine looks like:

The display has several parts. At upper left is the date and time; when the routine opens, it is initialized to the present (as determined from your computer's clock). Change the date and time by entering new values in the corresponding boxes and clicking the dark gray Recalculate button. Or click on the buttons in the next row to step backward or forward in increments of 1 day or 1 hour.

Our Saturn's Moons JavaScript uses Universal Time (UT, essentially the same as Greenwich Mean Time), and beneath the time buttons it shows what we think is the offset between UT and your local time, based on your computer's current settings. When changing the time manually using the Time input box, enter the Universal Time that corresponds to the local time when you will be observing. (Note that this works correctly only if your computer's clock is set properly, including an adjustment for daylight-saving time, if appropriate.)

At upper right is a diagram showing the positions of Titan, Rhea, Dione, Tethys, and Enceladus with respect to Saturn and its rings. Below the time buttons and the graphic are three buttons you can use to change the orientation of the diagram to match the view in your telescope. "Direct view" puts celestial north up and celestial east to the left; the routine opens in this orientation, which is the one used in star atlases. "Inverted view" puts south up and west to the left, matching the view seen in a Newtonian reflector in the Northern Hemisphere. "Mirror reversed" puts north up and west to the left, matching the view in most catadioptric (mirror-lens) and refractor telescopes used with a star diagonal in the Northern Hemisphere.

• Launch S&T's Saturn's Moons JavaScript

For more information about observing Saturn, see our online article:
"An Observing Guide to Saturn."